1. Field of the Invention
The present invention relates to a refrigeration system and more particularly to a refrigeration system able to achieve a temperature under 6 degrees Kelvin by the combination of a main-refrigerator and a sub-refrigerator.
2. Description of the Related Art
A conventional refrigeration system 500, as shown in FIG. 3, is disclosed in Japanese Utility Model Publication No. 43(1968)17026. In the refrigeration system 500, a first compression portion 501 which is formed by a piston 502 and a cylinder 503 is in fluid communication with a first expansion portion 504 which is formed by a piston 505 and a cylinder 506 via a heat exchanger 507, a regenerator 508 and a conduit 509. The conduit 509 is formed in a first cold-head 510.
Further, a second compression portion 511 which is formed by a piston 512 and a cylinder 513 is in fluid communication with a second expansion portion 514 which is formed by a piston 515 and a cylinder 516 via a heat radiation apparatus 517, a regenerator 518 and a conduit 519. The conduit 519 is formed in a second cold-head 520. The heat radiation apparatus 507 is thermally connected with the second cold-head 520. The pistons 502, 505, 512, 515 are driven by a driving means 521.
In the conventional refrigeration system 500, the diameter of each of the pistons 502, 505, 515 is constant from one end thereof to the other end thereof. Thus, atmospheric heat can invade the first compression portion 501, the first expansion portion 504 and the second expansion portion 514 via the pistons 502, 505, 515 due to heat conduction as the pistons reciprocate. So, the refrigerating capacity of the refrigeration system 500 is reduced.